Many industrial reactions, particularly those that involve the hydrogenation of organic compounds, are performed in stirred tank reactors employing a slurry catalyst system. Slurry catalysts are solid-phase, finely divided powders and are carried in the liquid reaction medium. The catalytic reaction is carried out, then, by contacting a reactive gas, such as hydrogen or oxygen, with the liquid organic compound in the presence of the solid-phase catalyst. On termination of the reaction, the catalyst is removed, generally by filtration, and the reaction product is recovered.
Slurry catalyst systems are inherently problematic in a number of areas, including industrial hygiene, safety, environmental, waste production, operability, selectivity and productivity. One problem, for example, is that these catalysts often are handled manually during a typical hydrogenation operation in a stirred tank reactor. Another is that many of the catalysts, hydrogenation catalysts in particular, are pyrophoric and thereby create additional safety concerns. These problems are compounded to a certain extent in that reaction rate often is a function of the catalyst concentration and, thus, catalyst concentrations generally are kept at high levels.
Monolith catalysts have been suggested for use in industrial gas-liquid reactions, but have achieved limited success. One of the advantages of monolith catalysts over slurry catalysts is that they eliminate the handling of powdered catalysts, including catalyst charging and filtration when the reaction is complete.
The following articles and patents are representative of catalytic processes including hydrogenation of organic compounds.
Hatziantoniou, et al. in xe2x80x9cThe Segmented Two-Phase Flow Monolithic Catalyst Reactor. An Alternative for Liquid-Phase Hydrogenations,xe2x80x9d, Ind. Eng. Chem. Fundam., Vol. 23, No.1, 82-88 (1984) discloses the liquid-phase hydrogenation of nitrobenzoic acid to aminobenzoic acid in the presence of a solid palladium monolithic catalyst. The monolithic catalyst consisted of a number of parallel plates separated from each other by corrugated planes forming a system of parallel channels having a cross sectional area of 1 mm2 per channel. The composition of the monolith comprised a mixture of glass, silica, alumina, and minor amounts of other oxides reinforced by asbestos fibers with palladium metal incorporated into the monolith in an amount of 2.5% palladium by weight. The reactor system was operated as a simulated, isothermal batch process. Feed concentrations between 50 and 100 moles/m3 were cycled through the reactor with less than 10% conversion per pass until the final conversion was between 50% and 98%
Hatziantoniou, et al. in xe2x80x9cMass Transfer and Selectivity in Liquid-Phase Hydrogenation of Nitro Compounds in a Monolithic Catalyst Reactor with Segmented Gas-Liquid Flowxe2x80x9d, Ind. Eng. Chem. Process Des. Dev., Vol. 25, No.4, 964-970 (1986) disclose the isothermal hydrogenation of nitrobenzene and m-nitrotoluene in a monolithic catalyst impregnated with palladium. The authors report that the activity of the catalyst was high and therefore mass-transfer determined the rate. Hydrogenation was carried out at 590 and 980 kPa at temperatures of 73 and 103xc2x0 C. Less than 10% conversion per pass was achieved.
U.S. Pat. No. 4,743,577 discloses metallic catalysts which are extended as thin surface layers upon a porous, sintered metal substrate for use in hydrogenation and decarbonylation reactions. In forming a monolith, a first active catalytic material, such as palladium, is extended as a thin metallic layer upon a surface of a second metal present in the form of porous, sintered substrate and the resulting catalyst used for hydrogenation, deoxygenation and other chemical reactions. The monolithic metal catalyst incorporates such catalytic materials such as palladium, nickel and rhodium, as well as platinum, copper, ruthenium, cobalt and mixtures. Support metals include titanium, zirconium, tungsten, chromium, nickel and alloys.
U.S. Pat. No. 5,063,043 discloses a process for the hydrogenation of anthraquinones using a monolithic reactor. The reactor is operated in a down-flow configuration, in which liquid is distributed to the top of the reactor, and hydrogen is drawn into the reactor by the action of gravity on the descending liquid. In the preferred implementation, in which there is no net pressure difference between the inlet and the outlet of the reactor, this mode of operation can be characterized as gravity downflow.
This invention relates to apparatus suited for gas-liquid reactions such as those employed in the hydrogenation or the oxidation of organic compounds and to a process for effecting gas-liquid reactions. The apparatus comprises the following:
a tank having at least one inlet for introduction of liquid, at least one outlet for removal of liquid, and at least one outlet for removal of gas;
a pump having an inlet and an outlet;
a liquid motive gas ejector having at least one inlet for receiving liquid, at least one inlet for receiving a reactant gas, and at least one outlet for discharging a mixture of said liquid and said reactant gas;
a monolith catalytic reactor having an inlet and an outlet;
wherein:
the inlet of said pump is in communication with said outlet from said tank for removal of liquid and said outlet of said pump is in communication with said inlet of said liquid motive gas ejector for receiving liquid,
the outlet from said liquid motive gas ejector for discharging the resultant mixture of liquid and gaseous reactant is in communication with the inlet to said monolith catalytic reactor and the outlet of said monolith catalytic reactor is in communication with at least one inlet to said tank, and,
the outlet from the tank for removal of gas is in communication with said inlet of the liquid motive gas ejector for receiving gas.
The apparatus described herein enables one to effect a catalytic retrofit of a slurry reactor and thereby offer many of the following advantages:
an ability to eliminate slurry catalysts and thereby minimize handling, environmental and safety problems associated with slurry catalytic processes;
an ability to interchange catalytic reactors when changing to a different chemistry in the same equipment;
an ability to effect multiple (sequential or parallel) reactions by using multiple catalytic reactors arranged either in series or in parallel;
an ability to maintain a separation of the reactants and reaction products from the catalyst during heat-up and cool-down and thereby minimize by-product formation and catalyst deactivation; and,
an ability to precisely start and stop a reaction by initiating or terminating circulation of the reactor contents through the liquid motive gas ejector and monolith catalytic reactor.